EFFECTS OF RADIATION
Reactor Water Chemistry
ON WATER CHEMISTRY (SYNTHESIS)
Both of these species are very reactive chemically, and there are several reaction pathways
available to each. Some of these mechanisms are very complex and are usually of little practical
value to the reactor operator, who is more concerned with the overall, observable effects. In
the case of water, the overall effect of irradiation is shown in the following reaction.
Because this result is not at all apparent from Reaction (3-1), the following section describes
the intermediate processes in some detail. This discussion is presented only to illustrate the
types of reaction mechanisms that occur in irradiated solutions. Subsequent discussions
primarily involve only the overall effects of these processes.
Reaction (3-1) shows that irradiation of pure water produces an electron and a H O ion. As
stated, both species are highly reactive. The H O ion rapidly reacts with a water molecule as
The species OH is an uncharged hydroxyl group. Neutral groups such as this, in which all
chemical bonding capacity is not satisfied, are common intermediate species in chemical
reactions and are called radicals or sometimes free radicals.
The electron produced by Reaction (3-1) first forms a species called the hydrated electron,
denoted by e
. The hydrated electron may be thought of as resulting from the interaction of
a negative electron with the positive end of a polar water molecule. This is analogous to the
formation of hydronium ions by interaction of a positive proton (H ) with the negative end of
a water molecule. Because the water molecules associated with hydrated electrons do not
participate in subsequent chemical reactions, they are not shown in chemical equations, and the
hydrated electron (e
) is used instead.
Hydrated electrons may interact with H O ions in solution or with water molecules. Both
reactions produce another reactive species, atomic hydrogen.
Reaction (3-4) usually predominates.